U.S. patent application number 14/371130 was filed with the patent office on 2015-01-08 for method of producing pressed paper piece and apparatus therefor.
This patent application is currently assigned to TOYO SEIKAN GROUP HOLDINGS, LTD.. The applicant listed for this patent is TOKAN KOGYO CO., LTD., TOYO SEIKAN GROUP HOLDINGS, LTD.. Invention is credited to Ichiro Kunihiro, Masahiro Ogawa, Seiji Okabe, Kenichi Takao.
Application Number | 20150008621 14/371130 |
Document ID | / |
Family ID | 48904968 |
Filed Date | 2015-01-08 |
United States Patent
Application |
20150008621 |
Kind Code |
A1 |
Takao; Kenichi ; et
al. |
January 8, 2015 |
METHOD OF PRODUCING PRESSED PAPER PIECE AND APPARATUS THEREFOR
Abstract
The objective of the present invention is to provide a method of
forming a pressed paper piece by deep drawing a sheet of blank that
is primarily made of paper in use of a punch and a die, and a
production apparatus for implementing the method, whereby no
distinguishable wrinkles are formed in upright portions of the
pressed paper piece. The method of producing a pressed paper piece
according to the present invention, implemented when deep drawing a
sheet-like blank that is primarily made of paper in use of a punch
and a die, includes maintaining a predetermined gap between a first
blank holder and the die in an outer peripheral region of a process
portion of the blank and applying a pressure to a radially inner
region thereof via a second blank holder, thereby reducing
wrinkling by an effect of integrated functions exerted in both
regions of the blank.
Inventors: |
Takao; Kenichi;
(Yokohama-shi, JP) ; Kunihiro; Ichiro;
(Yokohama-shi, JP) ; Ogawa; Masahiro;
(Yokohama-shi, JP) ; Okabe; Seiji; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYO SEIKAN GROUP HOLDINGS, LTD.
TOKAN KOGYO CO., LTD. |
Tokyo
Tokyo |
|
JP
JP |
|
|
Assignee: |
TOYO SEIKAN GROUP HOLDINGS,
LTD.
Tokyo
JP
TOKAN KOGYO CO., LTD.
Tokyo
JP
|
Family ID: |
48904968 |
Appl. No.: |
14/371130 |
Filed: |
January 10, 2013 |
PCT Filed: |
January 10, 2013 |
PCT NO: |
PCT/JP2013/050278 |
371 Date: |
July 8, 2014 |
Current U.S.
Class: |
264/323 ;
425/292 |
Current CPC
Class: |
B31F 1/0077 20130101;
B29K 2001/00 20130101; B31B 50/592 20180501; B29L 2031/7132
20130101; B29C 57/12 20130101; B29D 22/00 20130101 |
Class at
Publication: |
264/323 ;
425/292 |
International
Class: |
B31F 1/00 20060101
B31F001/00; B29C 57/12 20060101 B29C057/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 30, 2012 |
JP |
2012-016077 |
Claims
1. A method of producing a pressed paper piece, implemented when
deep drawing a sheet-like blank that is primarily made of paper in
use of a punch and a die, the method comprising: maintaining a
predetermined gap between a first blank holder and the die in an
outer peripheral region of a process portion of the blank and
applying a pressure to a radially inner region thereof via a second
blank holder, thereby reducing wrinkling by an effect of integrated
functions exerted in both regions of the blank.
2. An apparatus for producing a pressed paper piece by deep drawing
a sheet-like blank that is primarily made of paper in use of a
punch and a die, the apparatus comprising: means for maintaining a
predetermined gap S between a lower surface of a first blank holder
and an upper surface of the die during deep drawing, with the first
blank holder being arranged in an outer peripheral region of a
process portion of the blank, and a second blank holder having
pressing means being arranged in a radially inner region in the
process portion of the blank, wherein when the sheet-like blank is
not present, the second blank holder has a lower surface protruding
more than the lower surface of the first blank holder, with a
difference Z therebetween being S-T.ltoreq.Z<S, where T is the
thickness of the blank.
3. The apparatus for producing a pressed paper piece according to
claim 2, wherein the first blank holder has a sharp outer
circumferential edge that also serves as a cutter for cutting the
blank.
4. The apparatus for producing a pressed paper piece according to
claim 2, further comprising a lubricating oil supply member for
lubricating the upper surface of the die arranged opposite a lower
end face of the first blank holder.
5. The apparatus for producing a pressed paper piece according to
claim 3, further comprising a lubricating oil supply member for
lubricating the upper surface of the die arranged opposite a lower
end face of the first blank holder.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of producing a
pressed paper piece with less wrinkling, and an apparatus for
implementing the production method.
BACKGROUND ART
[0002] Pressed paper products have hitherto been universally used
as various forms of containers in the field of packaging and
containers. There are one-piece pressed paper items such as paper
trays or paper dishes, and two-piece containers such as paper cups
formed of a body member and a bottom member.
[0003] Pressed paper pieces formed by deep drawing a blank that is
primarily made of paper lack malleability and ductility unlike
metals and the blank tends to wrinkle in upright portions along the
peripheral edge, as the paper material is gathered together with
the reduction in diameter during the deep drawing process. FIG. 6
shows a common structure of a two-piece paper cup consisting of a
body member X and a bottom member Y. The bottom member, which is
the pressed paper piece, is formed by deep drawing. As shown in the
drawing, the lower end of the body member is folded back, and the
bottom member is jointed thereto by bonding, with the side wall of
the bottom member being sandwiched between the folded back
portions. Any wrinkles that are so large as to be folded over in
the side wall will cause an insufficient bond because of gaps in
the bonded surfaces. Such an insufficient bond would cause no
problem if the paper cup is disposed after holding a content liquid
that is immediately consumed. The paper cup, though, could not
withstand a long-term use as a container. The following techniques
are conventional methods of reducing wrinkles in pressed paper
pieces for ensuring that a good bond is formed.
[0004] Patent Document 1 discloses a method of producing a bottom
piece for paper cups, with an aim to produce a cup bottom such that
no wrinkles that are so large as to be folded over are formed when
compressing the rim of the bottom piece. The method includes:
applying a clamping force to an outer peripheral portion of a thick
circular paper stock; pressing a central portion of the paper stock
into a circular opening with a smaller diameter than that of the
paper stock while maintaining the clamping force to prevent
displacement of the outer peripheral portion, thereby to stretch
the paper stock; forming the rim, after the previous step of
stretching the paper stock, by reducing the clamping force
gradually and letting the outer peripheral portion enter the
opening and bend so that it extends substantially orthogonal to the
central portion.
[0005] Patent Document 2 aims at providing a leakage-proof bottom
paper piece fitted and bonded to a body section of a paper cup, and
shows a configuration wherein a through hole (female mold) is
formed in a mold section, and an annular pressing member driven by
a coil spring is arranged to press a bent portion of the bottom
paper piece against a stepped surface of the mold section. With the
bent portion being pressed by the pressing member, a punch (male
mold) is activated to deep draw the bottom paper piece. With this
configuration, as the bottom piece is gradually deep drawn while an
outer side of its bent portion is held down, narrow pleats-like,
easily-crushable folds are formed in the bent portion. As a result,
when joined by applying pressure, the bottom piece forms a
favorable tight bond with the body section, and thus highly
water-proof paper cup can be obtained.
[0006] Patent Document 1: Japanese Patent Application Laid-open No.
2000-238150 "Paper cup bottom and method and apparatus for forming
same", published on Sep. 5, 2000
[0007] Patent Document 2: Japanese Patent Application Laid-open No.
2001-270013 "Apparatus and method for forming bottom paper sheet of
paper cup" published on Oct. 2, 2001
DISCLOSURE OF THE INVENTION
[0008] For the pressed paper pieces made by the conventional method
of deep drawing while pressure is applied to the outer rim of the
circular blank, various techniques have been proposed such as
forming small wrinkles so as to form readily crushable folded
parts, or inserting the paper blank into a gap that is smaller than
the thickness of the blank during the deep drawing to crush small
wrinkles and to make them less notable. However, none of these
processes has been proven effective to completely eliminate
wrinkles.
[0009] Paper containers used in the field of food and drink
containers for a longer term than a normal storage period, i.e.,
long-life containers, are generally sterilized with the use of a
pharmaceutical agent. If the bottom member with wrinkles in the
side wall thereof is bonded to the body member, there will be gaps
near the joint between the side wall of the bottom member and the
body member on the side that contacts the contents, and this may
cause problems such as insufficient sterilization due to the
pharmaceutical agent failing to reach these parts, or the
pharmaceutical agent staying behind, or leakage of contents. A
forming method that can solve these problems and a production
apparatus for implementing this method are thus sought after.
[0010] An object of the present invention is to provide a method of
forming a pressed paper piece by deep drawing a sheet of blank that
is primarily made of paper using a punch and a die, and a
production apparatus for implementing the method, whereby the
problems described above are resolved, i.e., no distinguishable
wrinkles are formed in upright portions of the pressed paper
piece.
[0011] The method of producing a pressed paper piece according to
the present invention, implemented when deep drawing a sheet-like
blank that is primarily made of paper in use of a punch and a die,
includes: maintaining a predetermined gap between a first blank
holder and the die in an outer peripheral region of a process
portion of the blank and applying a pressure to a radially inner
region thereof via a second blank holder, thereby reduce wrinkling
by an effect of integrated functions working in both regions of the
blank.
[0012] The apparatus for producing a pressed paper piece by deep
drawing a sheet-like blank that is primarily made of paper in use
of a punch and a die, according to the present invention, includes:
means for maintaining a constant gap S between a lower surface of a
first blank holder and an upper surface of the die during deep
drawing, with the first blank holder being arranged in an outer
peripheral region of a process portion of the blank, and a second
blank holder having pressing means being arranged in a radially
inner region of the process portion of the blank, wherein, when the
sheet-like blank is not present, the second blank holder has a
lower surface protruding more than the lower surface of the first
blank holder, with a difference Z therebetween being
S--T.ltoreq.Z<S, where T is the thickness of the blank.
[0013] In the apparatus for producing a pressed paper piece
according to the present invention, in addition to the
configuration described above, the first blank holder has a sharp
outer circumferential edge that serves as a cutter for cutting the
blank.
[0014] The apparatus for producing a pressed paper piece according
to the present invention further includes a lubricating oil supply
member for lubricating the upper surface of the die arranged
opposite a lower end face of the first blank holder.
[0015] The method of producing a pressed paper piece according to
the present invention employs a configuration in which the gap
between the blank holder and the die is maintained constant in an
outer peripheral region of a process portion of the blank. As deep
drawing advances, the outer peripheral portion of the blank is
reduced in diameter, causing the blank to wrinkle, i.e., causing
the blank surface to warp, or causing the blank to increase its
thickness, so that the lower end face of the first blank holder
that was not in contact with the surface of the blank at first
comes to contact with the blank, whereby formation of wrinkles, and
in particular large wrinkles, is effectively prevented. This outer
peripheral portion of the process portion of the blank corresponds
to the side wall portion of the finished paper piece that is
radially compressed most and therefore prone to wrinkle, and
therefore preventing the wrinkling that occurs in an early stage of
the process with this first blank holder is of substantial
technical significance. The second blank holder, moreover, that is
located in the radially inner region thereof, applies pressure to a
portion that will be the upright portion of the pressed paper
piece, to prevent wrinkling in the middle stage of the process,
which is important to ensure a good bond with the body member and
to prevent formation of gaps near the joint. According to the
present invention, wrinkling is reduced by integration of these
functions of both blank holders, so that, even if there are
variations in blank thickness or fiber direction, the blank holder
that applies pressure in the inner peripheral region during the
deep drawing acts to reduce buckling (wrinkling) caused by the
circumferential compressive stress applied to the outer peripheral
portion of the blank in shrink flanging. Compared to the
conventional method of applying pressure to the entire outer
peripheral region, only the second blank holder applies pressure
according to the present invention, so that friction is reduced, as
a result of which the pressed paper piece is subjected to less load
during the process and is less likely to break.
[0016] Thus a desired pressed paper piece can be produced, as
wrinkling caused by insufficient pressure application, and rupture
caused by excessive pressure application, are effectively
prevented.
[0017] The apparatus for producing a pressed paper piece according
to the present invention includes, as described above, means for
pressing a sheet-like blank arranged in an outer peripheral region
of a process portion of the blank, wherein a first blank holder
that maintains a constant gap S between a lower surface thereof and
an upper surface of the die during deep drawing, and a second blank
holder arranged in a radially inner region thereof to apply
pressure to the sheet-like blank between itself and the upper
surface of the die, are arranged. When the sheet-like blank is not
present, the lower surface of the second blank holder protrudes
more than the lower surface of the first blank holder with a
difference Z being S-T.ltoreq.Z<S, where T is the thickness of
the blank. The relationship above defines the condition with which
wrinkle reducing pressure is applied by the second blank holder
during deep drawing and collision between the second blank holder
and the top surface of the die does not occur. Processing under a
setting in which the second blank holder collides the top surface
of the die raises the risk of pinching and of formation of
streamers and fines, and collisions that occur repeatedly,
immediately after each deep drawing and during no-load operation,
lead to deterioration of tool durability. The present invention
thus applies the condition above to avoid these problems.
[0018] In the apparatus for producing a pressed paper piece
according to the present invention, at the beginning of deep
drawing, only the second blank holder presses the outer peripheral
region of the process portion of the blank, but as deep drawing
advances, the outer peripheral portion of the blank is reduced in
diameter and gathered together, causing the blank to wrinkle, i.e.,
causing the blank surface to warp, or causing the blank to increase
its thickness, and when the warping or increased thickness exceeds
the size of the gap S, the first blank holder eventually applies
pressure for the wrinkle reducing effect. Since the gap S between
the lower surface of the first blank holder and the upper surface
of the die is maintained constant, the first blank holder thus
prevents wrinkling that occurs in an early stage of the process. As
the process proceeds further, the blank material disappears from
the region pressed by the first blank holder, and in the latter
half of the process, the pressure is only applied by the second
blank holder. With the apparatus for producing a pressed paper
piece according to the present invention, by these effects
described above, a pressed paper piece can be processed while
formation of distinguishable wrinkles in the upright portion of the
pressed paper piece is effectively prevented.
[0019] In the apparatus for producing a pressed paper piece
according to the present invention, in addition to the
configuration described above, the first blank holder has a sharp
outer circumferential edge to serve as a cutter for cutting the
blank, so that the apparatus is made compact.
[0020] Moreover, in the apparatus for producing a pressed paper
piece according to the present invention, a lubricating oil supply
member for lubricating the upper surface of the die is arranged
opposite the lower end face of the first blank holder. Thereby, an
appropriate amount of lubricating oil is applied on the lower
surface of the blank, so that friction between the die and blank
surfaces is reduced, to enable smooth deep drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a diagram illustrating an embodiment of the
apparatus of the present invention;
[0022] FIG. 2 is a diagram for explaining the forming process
according to the present invention;
[0023] FIG. 3 shows results of analysis from a CD direction of a
product processed according to the present invention;
[0024] FIG. 4 shows results of analysis from a CD direction of a
conventional product (1);
[0025] FIG. 5 shows results of analysis from a CD direction of a
conventional product (2); and
[0026] FIG. 6 is a diagram for explaining the structure of a
two-piece paper cup.
EXPLANATION OF REFERENCE NUMERALS
[0027] 1: first blank holder
[0028] 1a: lower end face of first blank holder
[0029] 1b: stepped portion of first blank holder
[0030] 2: second blank holder
[0031] 2a: lower end face of second blank holder
[0032] 2b: stepped portion of second blank holder
[0033] 3: die
[0034] 3a: upper surface of die
[0035] 4: pressure application mechanism
[0036] 4S: spring
[0037] 5: backing member
[0038] 6: cutter
[0039] 7: punch
[0040] 8: ejector member
[0041] 9: sheet-like paper material
[0042] 9a: blank
[0043] 10: lubricating oil supply felt
[0044] 50: pressing member with a constant gap of conventional
apparatus
BEST MODE FOR CARRYING OUT THE INVENTION
[0045] FIG. 1 shows the structure of processing parts of the
apparatus for producing the pressed paper piece according to the
present invention in cross section. The left side of the central
part shows a state before the processing, while the right side
shows a state during the processing. The lower left and right
diagrams each show enlarged views of essential parts, while the
upper left diagram shows part of the structure of a conventional
apparatus with a constant gap design. Reference numeral 1 denotes a
first blank holder, and 2 denotes a second blank holder. The second
blank holder 2 is arranged on the inner side of the first blank
holder 1, and their lower end faces are opposite the upper surface
3a of a die 3. A pressure application mechanism 4 is disposed in
this second blank holder 2 to apply a constant pressure. In the
example of configuration shown here, the pressure application
mechanism 4 is a spring 4s arranged between a backing member 5
integral with the first blank holder 1 and the second blank holder
2. While a spring is used as the pressure application mechanism in
this configuration, a pneumatic cylinder, a hydraulic cylinder, or
an elastic member such as rubber may also be used depending on the
pressure application capability and apparatus size.
[0046] Reference numeral 6 denotes an annular cutter placed on the
upper surface on the outer side of the die 3, which punches out a
blank from a sheet-like paper material in cooperation with the
first blank holder 1. The first blank holder 1 has a sharp outer
circumferential edge so that the paper material is cut clean.
Reference numeral 7 denotes a deep drawing punch, and 8 denotes an
ejector member fitted inside the lower end of the punch for
removing the pressed product from the die 3. In the state before
the processing in which the lower end faces 1a and 2a of the first
and second blank holders 1 and 2 are not in contact with the paper
material 9, the second blank holder 2 is pressed downward with a
predetermined force by the spring 4s arranged between the backing
member 5 integrally formed to the first blank holder 1 and the
second blank holder 2, as shown on the left side of the central
part of the drawing. The first and second blank holders 1 and 2
engage with each other at their stepped portions 1b and 2b so that,
as can be seen from the enlarged view shown in the lower left, the
lower end face 2a of the second blank holder 2 is located lower by
a difference Z than the lower end face 1a of the first blank holder
1. In the state in which the first blank holder 1 has moved
downward to punch out a blank 9a, or a piece that is going to be
processed, from the sheet-like paper material 9, as can be seen
from the enlarged view shown in the lower right, a constant gap S
is maintained between the lower end face 1a of the first blank
holder 1 and the upper surface of the die 3. With the first and
second blank holders 1 and 2 employing the configurations described
above, the apparatus could be designed to produce pressed paper
pieces of desired shapes without substantial remodeling of the
conventional apparatus, as there was no need to change the outer
shape of the pressing member 50 with a constant gap of the
conventional apparatus with a constant gap design shown in the
upper left of the drawing.
[0047] Reference numeral 10 in the drawing denotes an annular
lubricating oil supply felt arranged on the inner side of the
annular cutter 6 such that its upper surface is at the same height
as, and continuous with, the upper surface 3a of the die 3. While a
felt is used as the lubricating oil supply member in this
configuration, a porous member (metal, ceramics, plastics, and so
on), or an annular oil groove, for example, may also be used.
[0048] The lubricating oil supply member should preferably have a
smaller width than the width of the first blank holder 1. This is
because, if the lubricating oil supply member has a larger width
than that of the first blank holder 1 and is made of a soft
material such as felt, the pressure from the second blank holder 2
fails to be properly applied, as a result of which the intended
effect of reducing wrinkles may not be achieved, and also the
lubricating oil supply member itself may be damaged.
[0049] The operation according to the present invention will be
described with reference to FIG. 2. State (1) is the initial state
where the sheet-like paper material 9 has been fed to and placed on
the upper surface of the cutter 6. The first blank holder 1, second
blank holder 2, deep drawing punch 7, and ejector member 8 are
located at positions above the sheet-like paper material 9. State
(2) shows a blank 9a, or a piece that is going to be processed,
punched out from the sheet-like paper material 9. The first and
second blank holders 1 and 2 are integrally moved downward so that
the cutter 6 punches out a circular blank 9a from the sheet-like
paper material 9 in cooperation with the first blank holder 1. At
this time, as mentioned above, a constant gap S is maintained
between the lower end face 1a of the first blank holder 1 and the
upper surface of the die 3 (see FIG. 1), and the lower end face 2a
of the second blank holder 2 is located lower by a difference Z
than the lower end face 1a of the first blank holder 1, so that the
relationship of S.ltoreq.T+Z is established, wherein T is the
thickness of the sheet-like paper material 9 (see FIG. 1).
Therefore, the lower end face 1a of the first blank holder 1 is not
in contact with the surface of the sheet-like paper material 9,
while the lower end face 2a of the second blank holder 2 is
applying a pressure on the surface of the sheet-like paper material
9 as given by the spring 4s. With this pressure being applied to
the periphery of the circular blank 9a by the second blank holder
2, the process proceeds to an initial step of deep drawing shown as
State (3). In this step, the deep drawing punch 7 and the ejector
member 8 are integrally lowered to press a central portion of the
blank 9a against the inner circumferential surface of the die 3 to
start deep drawing. At first the first blank holder 1 has no
bearing on the blank 9a since its lower end face 1a is not in
contact with the surface of the blank 9a. As deep drawing advances,
however, the outer peripheral portion of the blank 9a is reduced in
diameter, causing the blank to wrinkle and the blank surface to
warp or causing the blank to increase its thickness, and eventually
contacts the lower end face 1a of the first blank holder 1. This
contact effectively prevents large wrinkles from being formed
during wrinkling.
[0050] At this point, the lubricating oil supply felt 10 is in
contact with the lower face of the outer peripheral portion of the
blank 9a and applying lubricating oil in this region. As deep
drawing proceeds, the blank 9a reduces in diameter, and its outer
peripheral portion moves from a region under the lower end face 1a
of the first blank holder 1 to the region under the lower end face
2a of the second blank holder 2, so that lubricating oil is
distributed entirely over the area where the die 3 contacts the
blank 9a, to reduce contact friction.
[0051] State (4) shows a middle step of the deep drawing process.
The punch 7 and the ejector member 8 are integrally lowered further
into the die 3 and the side wall of the bottom member is being
formed between the punch and die. Deep drawing proceeds, with a
constant pressure being applied on the outer peripheral portion of
the blank 9a on the upper surface of the die 3 from the lower end
face 2a of the second blank holder 2 as given by the spring 4s. It
is the major characteristics of the present invention that this
pressure provided by the spring 4s is always constant irrespective
of the thickness of the blank 9a. In the conventional apparatus
wherein the gap between the blank holder and the upper surface of
the die was constant, the pressure applied on the outer peripheral
portion of the blank 9a varied depending on the variations in
thickness of the material of the blank 9a itself or changes of
thickness during the process, which caused problems such as rupture
or insufficient pressure application. The present invention employs
a pressure application mechanism 4, which is the spring 4s in this
embodiment, whereby a constant pressure is applied even if the
thickness of the blank 9a varies, so that thickness variations are
absorbed by displacement of the second blank holder 2. State (5)
shows the last step of the deep drawing process. The outer
peripheral portion of the blank 9a has come off of the lower end
face 2a of the second blank holder 2 and been drawn onto the inner
circumferential surface of the die 3 to be the side wall of the
bottom member, whereupon the deep drawing is complete. State (6)
shows the removal of the pressed paper piece (bottom member in this
embodiment) that has been deep drawn from the die. The ejector
member 8, which was fitted in the punch 7, separates from the punch
7 and moves downward independently, to eject the pressed paper
piece formed inside of the die 3. After deep drawn, the pressed
paper piece thus obtained according to the present invention,
although not shown, is then inserted into a tubular body member,
and the wall portion of the pressed paper piece is joined to the
side wall of the body member to produce a paper container.
EXAMPLES
[0052] A comparison was made of an already commercially available
pressed paper piece produced by a conventional method (Conventional
product 1), a pressed paper piece formed by the method described in
Japanese Patent Application Laid-open No. 2001-270013 (Conventional
product 2), and the pressed paper piece made by the production
method of the present invention.
[0053] Paper stock with a base weight of 200 g/m.sup.2 and
laminated on each side with polyethylene was used as the blank, and
a paraffin-based adhesive was used during forming. The adhesive is
one that is commonly used for paper cups. A spring mechanism was
employed for the mechanism that allows displacement of the blank
holder relative to the top surface of the die 1 while a constant
pressure is being applied to the outer peripheral portion of the
blank 9a. The following other conditions were set the same:
[Shared Conditions]
[0054] Blank diameter: 065 mm Blank thickness: T=0.37 mm Die hole
diameter: .phi.47.1 mm Die shoulder radius: 1.5 mm Punch outer
diameter: .phi.46.0 mm Pressing speed: about 360 mm/sec
[0055] Next, the working conditions of the present invention,
Conventional product (1), and Conventional product (2) are shown in
Table 1. "Wrinkle reducing pressure" here refers to the pressure
applied from the second blank holder to the blank in an early stage
of the processing.
TABLE-US-00001 TABLE 1 Present Conventional Conventional Invention
Product (1) Product (2) Wrinkle First Present Absent Integral
Reducing Blank Method holder Second Present Present Blank holder
Size Of Outer .phi.65 mm -- .phi.65 mm First Diameter Blank Inner
.phi.56.2 mm -- -- holder Diameter Size Of Outer .phi.56 mm .phi.56
mm -- Second Diameter Blank Inner .phi.48 mm .phi.48 mm .phi.48 mm
holder Diameter Gap S Between Die 0.38 mm -- 1.00 mm Upper Surface
And First Blank holder Difference Z 0.05 mm -- -- Wrinkle Reducing
3.3 MPa 3.3 MPa -- Pressure
[0056] Mechanical properties of deep drawn pieces of paper blank
differ depending on the orientation of paper fibers. As the paper
is made by flowing pulp through the paper making machine in a
predetermined direction, the fibers tend to align themselves with
the advancing direction, which is called the "grain direction of
paper". The sheet-like paper material 9 in the present invention is
fed along this grain direction of paper, i.e., along the direction
in which the fibers are aligned, and this direction will
hereinafter be referred to as "MD direction", while the direction
orthogonal thereto will be referred to as "CD direction". The paper
is intrinsically strong in the MD direction as it hardly stretches
in this direction, while it can stretch and is easy to break and
wrinkle in the CD direction.
[0057] In FIG. 3, A is a photograph taken from the CD direction of
the pressed paper piece of the present invention. Pictures were
taken only from the CD direction, in consideration of the paper
characteristics noted above, as wrinkling is more likely to occur
in the CD direction. The paper piece has a smooth surface and no
wrinkles are visually perceptible. For more detailed evaluation, it
was observed with a scanning electron microscope at 50 times
magnification.
[0058] In FIGS. 3, C, D, and E are microscopic photographs of a
side wall cross section at 2 mm height from the bottom (CD_2), a
side wall cross section at 5 mm height from the bottom (CD_5), and
a side wall cross section at 1 mm height from the upper end
(CD_m1), as indicated in diagram B. All the cross sections were
observed from the upper end side. No wrinkles are found in CD_2 and
CD_5. In CD_m1, although fine dents were perceptible, no
folded-over portions were present.
[0059] In FIG. 4, A is a photograph taken from the CD direction of
Conventional product (1). Wrinkles are visually perceptible.
Similar observation revealed that small dents were present in CD_5,
which developed into wrinkles in CD_m1 larger than those at the
corresponding position of the pressed paper piece of the present
invention.
[0060] In FIG. 5, A is a photograph taken from the CD direction of
Conventional product (2). Large wrinkles are clearly visible.
Observation was made similarly except that, instead of CD_m1 as in
FIG. 3, the cross section of the side wall at 8 mm height from the
bottom (CD_8) was observed, which revealed that large,
distinguished wrinkles had formed in all the cross sections.
[0061] As shown by the results described above, the pressed paper
piece of the present invention not only has a better finished
surface but also has much less wrinkling than conventional
products, which enables a reliable bond to be formed with another
component such as a body member without cavities or the like in the
adhesive layer, and so a desirable paper container that can
withstand long-life applications can be provided.
INDUSTRIAL APPLICABILITY
[0062] Although the invention has been described herein with
respect to an example of forming the bottom part of a paper
container such as a paper cup, the invention is not limited to the
bottom part of two-piece paper containers but may also be applied
to one-piece paper containers with side walls of a small height
such as paper dishes or paper trays. The pressed paper piece or
paper container of the present invention may contain drinks such as
milk, milk for use in portions, coffee, or food products such as
jam, yogurt, cheese, butter, ice cream, or snack food.
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